Metal fabrication



Oct. 23, 1962 w. c. BELL ET AL 3,059,503

METAL FABRICATION Filed Feb. 28, 1958 FIG. III

INVENTORS WILLIAM C. BELL JOSEPH M. LUI NO B Q 6 ATTOR Y United StatesThis invention relates to the shaping or drawing of sheet material intopredetermined form, and more particularly to an improved method of andapparatus for forming sheet material into desired shapes preciselyconforming to the forming surface, thus eliminating the neoessity forhand finishing operations.

The so-called Guerin process of forming and shearing sheet metal intodesired shape has long been known to industry, and a number of patentshave been issued thereupon. The apparatus used in such a processincludes a support or table adapted to support a die about which themetal sheet may be formed, and a head member movable toward the table.Secured to the head member is a block or body of fluid-like, fiowablematerial such as rubber, which has a tendency to deform in a manner tosurround a body against which it is pressed. To restrain the fiowablematerial from lateral flow when it is under vertical pressure, it isconfined within a box or wall so that the material is contained within acornpletely closed space prior to and during the time it is inengagement with the die and the upper surface of the table. The processconsists essentially in placing a sheet of metal over the die andforcibly applying pressure through the head member to the metal sheet tocause it to assume a shape as near as possible to the contour of thedie.

The foregoing process has many advantages, particularly when it isdesired to form a small number of metal parts, since the need for therelatively expensive cornpanion punch and die members, and the skill andtime required to dispose them in mating relationship in ordinary punchpresses is eliminated. Its disadvantages reside in the fact thatextremely high forming pressures cannot be applied directly to thematerial to be formed, for due to the lateral flow tendency of therubber, unsatisfactory and incomplete formation of the shaped articlesis often obtained, which results in expensive hand operations necessaryto form the article to required shape. In addition, due to compressionof the sheet, wrinkles in the shaped article are frequently encountered,which also necessitates a hand finishing operation. The fact that afluid-like material such as rubber is used in the head member oftenresults in inadequate formation of the lower portion of the shapedarticle. This is especially true when the article being formed has sidewalls or flanges, for the side walls are always under inadequatepressure, which permits them to spring back when the article is removedfrom the forming surface.

Various prior art arrangement have been directed to solving the problemof preventing the wrinkling and/or spring-back of flanges, but in eachknown instance the solution necessitated the use of an expedient such asa clamping ring to hold the edge of the sheet to prevent it fromwrinkling while the article is being formed, or an edge restrainingmember arranged to recede in the direction of the applied pressure insuch a manner that the flanges will be properly supported during theoperation. However, such apparatus has been comparatively complicated,necessitating a substantial amount of time for adapting the hydraulicpress or drop hammer for the particular operation.

Therefore, the solution commonly resorted to in the aircraft industryfor the manufacture of aircraft parts atent ice such as gussets, noseribs, frames and the like has been to employ two form blocks or dies forthe manufacture of such parts. The sheet material to be formed was cutapproximately to the proper size and then placed upon the first formblock. A hydraulic press or drop hammer was then employed to shape thesheet material to the proper configuration, this more specifically beingaccomplished by placing the first form block (known as a spring-backblock) upon the base or platen of the press, and then lowering the presshead so as to cause the sheet material to assume the configuration ofthe block. It has been found from experience that if any substantialforming of the part was involved, it was then necessary to transfer thepart to the second form block ('known as a hammer block) for thefinishing operation. This latter block is made closely to engineeringdimensions, and the part was placed upon it and a rawhide hammer, woodenmallet or the like was then employed for finish forming the part,thereby to eliminate wrinkles and any springback of the flanges. Thisfinish forming step was very expensive, for it delayed production,required double tooling, and involved considerable labor costs.

According to the present invention, articles may be formed of sheet at arapid rate in a straightforward, uncomplicated manner, using a singleform block, with the elimination of prior art hand finishing operations.Furthermore, no time is required to adapt the press or hammer for theforming operation according to this invention, for the single formingblock or die block can be placed directly upon the base of the press orhammer, without the necessity for employing any other tooling.

The process for forming an article according to this invention may becarried out utilizing a hydraulic press or drop hammer, and involves theuse of an underlay in conjunction with the article or part being formed,as well as, in most instances, an overlay. More specifically, thisprocess involves placing the underlay, such as of thin aluminium, uponthe form block, the underlay conforming quite closely to the activesurfaces of the block. The sheet to be formed is then placed upon theform block in the proper manner, and then the overlay, such as ofplastic, may be placed on the sheet. To facilitate alignment of theseveral components, on the form block two or so locating pins arepreferably utilized, to project upwardly through tooling holes providedin the components to be placed upon the block. The press head press padhaving the general characteristics of rubber is then moved toward theforming block so as to initially form the sheet. The several componentsare then removed from the form block, the underlay set aside, and thearticle to be formed fitted directly upon the forming block so that itcan be resubjected to the pressure of the press head whereby to finishform the article. As in the initial forming step, the overlay again maybe utilized between the press head and the article to improve upon theaction of the captive rubber head.

It will be observed that the foregoing method involves the simplest ofmaterials and tools, it being unnecessary to utilize complicated, priorart expedients. Because of the presence of the underlay, the initialforming of the article according to this invention results in the sidewalls or flanges being formed somewhat less severely than required bydesign standards. Therefore, when the underlay is removed and thearticle restruck, the result is that the extent of curvature of theflanges of the article will be increased, and the article caused toconform pre: cisely to the contour of the forming block, with notendency of the flanges to spring back away from the desiredconfiguration. The use of the overlay enhances the action of the captiverubber head upon the part being formed, for instead of flowing out ofthe way as rubber does rather it is firm enough to assure accurateconforming of the article to the forming block, for it pushes andcompresses the sheet in such a manner as to eliminate wrinkles.

If heat treating of the articles is involved, such as when 6061-80aluminum is being used, the aluminum is preferably in the annealedcondition during the forming operation, with the heat treating and agehardening steps being performed afterward. However, depending upon thesize of the article being formed and the complexity of the formingoperation, it may be desirable to heat treat the article before theinitial forming operation, or between the initial forming operation andthe final forming operation.

The invention will now be further described in conjunction with thedrawings wherein:

FIGURE I shows in exploded relation the forming block, underlay, articlebeing formed, and the overlay;

FIGURE II illustrates to a somewhat different scale the cross sectionalview of a forming machine, indicating the placement of the underlay uponthe form block, and sheet material in the unformed condition restingupon the underlay; and

FIGURE III illustrates a view taken before the second forming operation,showing the article being formed resting upon the form block with theoverlay in place thereon.

In FIGURE I, a nose rib is being manufactured, with the basic componentsinvolved in the operation being a forming block or die 10, underlay 11,article 12 being formed (i.e. nose rib), and overlay 13. The formingblock is to be placed upon the base or platen 14 of a hydraulic press15, with underlay '11 fitted upon the block 10 in the manner shown inFIGURE II. The sheet material 12, cut approximately to size, is placedupon the underlay with the margins overhanging the sides of the block.The press head 16 shown in FIGURE II can be operated to bring the blockor body of rubber or other elastic or fluid-like material 17 intocompressive cont-act with material 12, to form it into the desiredshape. In most instances, it is desirable in the practice of thisinvention to use an overlay 13 to prevent lateral flow of therubber-like material 17 from occurring. So that the components 11, 12'and 13 can be maintained in proper alignment upon block 11, two or solocating pins 18 may be provided upon block 10, which are adapted toproject through tooling holes in the component conveniently provided.

Upon the components being assembled in the manner shown in the drawing,the head 16 of the press or drop hammer is lowered so as to cause thearticle to conform precisely to the configuration of the active surfacesof underlay 11 resting upon the forming block with the result being theformation of an article 12' as illustrated in exploded relation inFIGURE I. The underlay 11 is then removed, and the article 12 replaceddirectly upon the forming block, with the relationship of the article12' and overlay 13, if used, being approximately that illustrated inFIGURE III. The head is then lowered again to further shape the article12, this causing the flanges to closely assume the configuration of theforming block, after which the flanges do not tend to spring back intothe position of the flanges before the final forming.

As to the underlay, thin aluminum is quite satisfactory for thispurpose, in which event, it may be formed simultaneously with theforming of the first article 12' being manufactured. It will, of course,be obvious that after the first forming operation, the underlay willhave assumed the configuration of the form block, and in most instancesan underlay may be used many thousands of times for subsequent formingoperations.

As to the overlay, plastic is preferred, such as polyvinyl chloride inapproximately inch or 4 inch thickness. A vinyl marketed under the tradename Vyflex" has been determined to be highly successful for thispurpose. When thick vinyl is being used, the vinyl is preferably heatedto approximately 300 F. preparatory to the first stroke, but after thatthe vinyl hascurled or bent edges and may continue to be used a largenumber of times.

Sheet material of a large number of different aluminum alloys has beensuccessfully employed, such as 7075, 2024, etc. Although such is morediflicult, this invention may also be used for the forming of othermetals such as some alloys of titanium or steel, as well as for theforming of other sheet materials.

When aluminum articles are being manufactured, the metal preferably isin the annealed (SO) condition, with heat treating and age hardeningsteps being performed according to the size and complexity of the part.As a first example, if a small heavy part is being formed, after theperformance of the first forming step utilizing the underlay, thearticle may then be heat treated at approximately 900 F. forapproximately 20 minutes, and then free-fall quenched. The second orfinal forming operation is then performed without using the underlay,this latter forming operation serving the double purpose of eliminatingdistortion caused by the heat treating, as well as finish forming thepart. The article is then aged at approximately 300 F. for approximately8 hours so as to bring it up to full hardness.

As another example, if large thin parts are to be formed, the annealedmaterial is initially heat treated at approximately 900 F. forapproximately 20 minutes before either of the forming operations, forheat distortion in large thin parts is typically so severe that theymust be level rolled prior to either of the forming operations.Therefore, the first forming operation would be performed in theas-quenched condition with the underlay in place, and immediatelythereafter, the second forming operation is performed without using theunderlay. It should be noted that these operations should be performedwithin a thirty minute period following the 900 F. heat treating. Afterthe second forming operation, the part is then placed in a furnace atapproximately 300 F. for eight to twenty-four hours so as to bring thematerial to the T6 or full hardness condition. As is to be noted, theheat treat process may be performed before the initial formingoperation, between the initial and final forming operations, or afterthe final forming operation.

This invention has been successfully used with a variety of sheetmaterials for the formation of both large and small items. As an exampleof large items, frames for aircraft have been manufactured which measure4' by 8' and larger.

We claim:

1. A process of forming a sheet into a flanged article comprisingplacing an underlay upon a forming block, placing the sheet thereupon,with an edge portion of the sheet projecting from the edge of saidforming block, placing a plastic overlay upon said sheet, moving a bodyof flowable material toward said forming block so as to initially flangesaid sheet, and conform it to the general contour of said forming block,removing said underlay, said sheet and said overlay from said formblock, and replacing said sheet directly upon said form block, replacingsaid overlay, and then resubjecting said sheet to the pressure of saidflowable material whereby to finish form said article, and thereby makeunnecessary any hand finishing to eliminate springback of the flangesthereof.

2. The process as defined in claim 1 wherein said article to be formedis heat treated in the interval between initial forming and finishforming.

3. The process defined in claim 1 in which said article to be formed isheat treated after finish forming thereof.

4. A die set for producing marginally flanged sheet metal parts infinished condition comprising a forming block having top and sideportions adapted for the forming of sheet metal parts, a comparativelythin reuseable metal underlay adapted to be fitted upon said formingblock during the initial forming of a part, and to be removed therefromduring finish forming of the part, and a rubber die member movable intoengagement with said part to conform it to the shape of the underlayduring the initial forming step, and to the shape of the forming blockduring the finish forming thereof, whereby to form metal parts needingno hand finishing.

5. A die set for producing marginally flanged sheet metal parts infinished condition comprising a forming block having top and sideportions adapted for the forming of sheet metal parts, a comparativelythin reuseable metal underlay adapted to be fitted upon said formingblock during the initial forming of a part, and to be removed therecfromduring finish forming of the part, a plastic overlay to be placed uponsaid part to be formed during both the initial forming and final formingthereof, and a rubber die member movable into engagement with saidplastic overlay to conform said part to be formed to the shape of theunderlay during the initial forming step, and to the shape of theforming block during the finish forming thereof, whereby to form metalparts needing no hand finishing.

6. The process of forming marginally flanged articles which consists inlaying sheet material on an underlay residing upon a rigid formingblock, with the margins of the material overhanging the sides of saidunderlay, forcing a confined body of fiOW2Jbl6 material againstsubstantially the entire area of the upper surface of the sheet materialwith sufficient pressure to bend said overhanging margins against thesides of said underlay and conform it to the top and sides of saidunderlay, removing the article so formed of sheet material and theunderlay from said block, and then replacing the article directly uponsaid block, again forcing said confined body of flowable materialagainst substantially .the entire area of the article so as to conformit to the active sides of said block forming whereby said flanges willbe wrinklefree and have no tendency to spring back away from the desiredconfiguration.

7. The process as defined in the claim 6 in which an overlay is placedbetween said sheet material and said confined body of fiowable materialduring said forming operations.

8. The process as defined in claim 6 in which the article to be formedis heat treated before the step of forming upon said form block withoutsaid underlay.

9. The process as defined in claim 6 in which the article to be formedis heat treated after the secondrecited forming step.

References Cited in the file of this patent UNITED STATES PATENTS2,140,131 Helfrick Dec. 13, 1938 2,390,803 Marschner Dec. 11, 19452,434,379 Wiesner et al. Jan. 13, 1948 2,565,949 Cliiford et al Aug. 28,1951 2,688,297 Livermont et al. Sept. 7, 1954 2,719,500 Kraybill Oct. 4,1955 2,736,674 Harmon Feb. 28, 1956 2,741,205 Paulton Apr. 10, 19562,761,405 Moller Sept. 4, 1956 2,762,734 Corral Sept. 11, 1956 FOREIGNPATENTS 716,480 Ger-many Jan. 21, 1942 OTHER REFERENCES The ModernIndustrial Press, September 1947, pages 6, 8 and 20.

